Two-stroke internal combustion engines



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Oct. 23, 1962 P. L. ,TORRE 3,059,624

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TWO-STROKE INTERNAL COMBUSTION ENGINES Filed June 8, 1961 3 Sheets-Sheet3 Fig. 3

United States Patent 3,059,624 TWO-STROKE INTERNAL COMBUSTION ENGINESPier Luigi Torre, Milan, Italy, assignor of one-half to Innocenti Soc.Gen. per PIndustria Metallurgica e Meccanica, Milan, Italy Filed June 8,1961, Ser. No. 115,761 Claims priority, application Italy June 15, 19604 Claims. (Cl. 123-59) This invention relates to two-stroke internalcombustion engines of the character wherein fuel mixture is drawn from acarburetor to the crankcase of the engine through a non-return valve oncompression stroke and is compressed in the crankcase and ultimatelytransferred to the cylinder during expansion stroke.

In bi-cylindrical engines of the character mentioned above a partitionis provided in the crankcase accommodating an intermediate bearing forthe crankshaft and sub-dividing the crankcase into two pre-compressionchambers associated with the respective cylinders, each of the twopre-compression chambers connecting with the carburetor through its ownnon-return valve and through a common induction passage extending fromthe valves to the carburetor.

Serious difliculties have been encountered in practice in the attempt ofreducing the pressure drop across the valves as far as possible therebyto improve the filling factor of the engine. Reed-valves have beenemployed to this end, having low inertia and ofiering relatively largeports for the flow of fuel mixture.

-It is an object of this invention to still more increase the overallarea of the ports thereby to substantially increase filling thepre-compression chambers hence efficiency of the engine.

Another object of the invention consists in providing a non-return valveunit for the cylinder or each cylinder of the engine which is easilyassemblable and exchangeable when necessary.

Further objects and characteristic features of the invention will resultfrom the following description wherein reference is made to theaccompanying drawing, in which:

FIG. 1 is a vertical sectional view of a two-cylinder twostroke engineembodying the invention;

FIG. 2 is a vertical sectional view of a one-cylinder engine, and

FIG. 3 is a cross sectional view on line IHIH of FIG. 2.

Referring to FIGURE 1, the engine shown comprises an engine block Ahaving a crankcase B fluid-tight bolted thereto and a pair of cylindersC in in-line arrangement, one only of the cylinders being thereforevisible on the drawing. =A crankshaft extends perpendicularly to theplane of the figure including a pair of crankpins D associated with therespective cylinders C and an intermediate bearing journal D thecrankpins D being operatively connected by means of connecting rods Ewith pistons F reciprocable in the respective cylinders.

The intermediate journal D is rotatably supported by a plain bearing Mmounted in a transverse partition L which is cast-formed both in theengine block A and crankcase B. In this manner each of the cylinders hasan underlying pre-compression chamber associated therewith. A section ofthe partition which is adjacent the bottom B of the crankcase inenlarged to thereby enclose a pair of co-axial outwardly openingcylindrical seatings 3, 3, the common axis of which extends transverselyof the crankshaft axis beneath the bearing M.

Two independent valve bodies 21 are inserted into respective seats 3.The valve bodies each comprise a prismatic flat-face middle portion 21and two cylindrical end flanges 22, 23. A sealing ring 11 is provided oneach inward flange 22.

The seats 3 connect with respective pre-compression chambers andcomprise each a middle cylindrical portion 3a as obtained from castingand two machined cylindrical end portions 3b, 36, which are larger andsmaller in diameter, respectively, than the middle portion 3a. Theportion 3c of the seat 3 receives in a fluid-tight relation the flange22 with its sealing ring .11.

The flange 23 is received by the portion 3b of the respective seat 3 andis formed with an outer bead 23a to thereby act as a cover sealed by aflat annular seal 24.

An inwardly flaring recess 5 is formed within each of the valve bodiesand opens on the inward flange 22 to connect with an induction conduit 6leading to a carburetor, the conduit 6 being formed in the crankcasefrom the bottom of the latter towards bearing M.

Transverse apertures 7 extend from the recess 5 perpendicular to theflat opposite faces of the prismatic portion 21 of the valve body. Theapertures are controlled by reeds 8 in a manner known in the art,providing nonreturn valves between the conduit 6 and respective precompression chambers in the crankcase which open during the compressionstroke of the respective piston to allow flow of fresh mixture from thecarburetor to said precompression chamber.

It will be seen that the seats 3, 3 leave therebetween a solid portion.25 in the crankcase supporting the bearing M to thereby reinforce thisregion of the crankcase against thrusts applied thereon by thecrankshaft.

In addition to the objects and advantages set out in the preamble theabove described arrangement aifords the further following advantages:

(a) Base in assembly of the valve bodies with their seals, for the axialpressure required for assembling the valve bodies into their seats actsonly at the end of the necessary axial displacement to engage thecylindrical flanges 22, 23 of the valve bodies in the machined sections3b, 3c of the seats. Wear on the sealing ring 11 during assembly isthereby insignificant.

(b) The machined surfaces 3b, 30 on the seat are of limited area andrequire thus a limited work only.

(0) Each valve body feeds its own cylinder.

According to the modification shown in FIGURES 2 and 3 which refer to aone-cylinder engine and in which similar references are used to denoteparts similar to those shown on FIG. 1, the non-return valve unitcomprises a single valve body 21, 22, 23 of the previously describedtype, arranged in a seat formed transversely beneath one of the journalbearings M for the engine shaft (FIG. 3).

In use in connection with one-cylinder engines the further followingmain advantages are obtained.

(1) The valve body is angularly so positioned in its seating 3 that theintake passages controlled by the reeds 8 open in the direction towardsthe overflow conduit, so that the mixture flowing to the precompressionchamber does not undergo any sharp change in direction to enter theconduit. I

(2) The sense of rotation of the engine shaft is advantageously selectedso that on rotation its cranks generate at the valve region anunderpressure which furthers the mixture admission to the precompressionchamber.

(3) The arrangement of the valve is such that during suction of thefresh mixture before the latter enters the overflow conduit it directlyimpinges upon the crank pin and big end of the connecting rod, therebyimproving lubrication and cooling of the said components.

(4) The solid portion 25 provides a curved baffle (FIG. 2) for themixture flow entering the recess 5, in the valve body, thereby avoidingwhirling.

What I claim is:

1. A two-stroke internal combustion engine comprising an engine blockhaving a cylinder therein, a crankcase having a bottom wall, the saidengine block and crankcase jointly enclosing a pre-compression chamber,a crankshaft rotatable in the chamber, a journal bearing for thecrankshaft jointly supported by the engine block and crankcase, acylindrical axially elongated seating formed in the crankcase on an axiswhich is transverse to the longitudinal axis of the crankshaft and islocated between the said journal bearing and bottom wall of the crankcase, the said seating including an outwardly opening first cylindricalend section, a cylindrical inner end section of a diameter smaller thanthat of the said first cylindrical end section and an intermediatecylindrical section of a diameter the value of which is intermediate thevalues of the diameters of the two end sections, the said intermediatecylindrical section opening into the pre-compression chamber, anon-return reed-valve unit axially inserted into the seating, the saidvalve unit including a valve body comprising a pair of end flangesengaging with respective cylindrical end sections of the .seating and aflattened intermediate section substantially co-extensive axially withthe intermediate section of the seating, a cavity extending into theintermediate section of the valve body through axially inner flange ofthe body, reed-controlled apertures in the saidsintermediate section ofthe body providing an intake-connection between the cavity and theintermediate section of the seating, and an intakepassage through thebottom wall of the crankcase connecting with the said cavity in thevalve body.

2. In the internal combustion engine as claimed in claim 1, acircumferential bead on that flange on the body which engages in theoutwardly opening first cylindrical end section of the seating, and asealing ring axially compressed between the said bead and the crankcase.

3. A two-stroke internal combustion engine comprising an engine blockhaving a pair of in-line cylinders therein, a crankcase having a bottomwall, the said engine block and crankcase jointly enclosing a chamber, acrankshaft rotatable in the chamber including a pair of cranks and anintermediate journal, a transverse partition in the said chamberextending between the pair of cranks subdividing the chamber into a pairof pre-compression chambers associated with the respective cylinders, apair of cylindrioal axially aligned seatings formed in the partition onan axis which is transverse to the longitudinal axis of the crankshaftand is located between the said intermediate journal and bottom wall ofthe crankcase, each of the said seatings including an outwardly openingfirst cylindrical end section, a cylindrical inner end section of adiameter smaller than that of the first cylindrical end section and anintermediate cylindrical section of a diameter the value of which isintermediate the values of the diameters of the two end sections, theintermediate cylindrical section in each seating opennig into itsrespective pre-compression chamber, a pair of non-return reedvalve unitsaxially inserted into respective seatings each of which includes a valvebody comprising a pair of end flanges engaging with respectivecylindrical end sections in the respective seating and a flattenedintermediate section substantially co-extensive axially with theintermediate section of the seating, a cavity extending into theintermediate section of the body through axially inner flange of thebody, reed-controlled apertures in the said intermediate section of thebody providing an intake-connection between the cavity and theintermediate section of the seating, and an intake-passage through thebottom wall of the crankcase connecting with the cavities in the twovalve bodies.

4. In the internal combustion engine as claimed in claim 3, acircumferential bead on that flange of each valve body which engages inthe outwardly opening first cylindrical end section of the seating, anda sealing ring axially compressed between the said bead and thecrankcase.

References Cited in the file of this patent UNITED STATES PATENTS2,973,752 Torre Mar. 7, 1961

